Imaging device and digital camera using the imaging device

ABSTRACT

An imaging device has a zoom lens system having a plurality of lens units and forming an optical image of an object so as to continuously optically zoom by varying distances between the lens unit; and an image sensor converting the optical image formed by the zoom lens system to an electric signal. The zoom lens system has from an object side, a first lens unit being overall negative and including a reflecting surface that bends a luminous flux substantially 90 degrees; and a second lens unit disposed with a variable air distance from the first lens unit, and having an optical power, and wherein at least one lens element made of resin is included in the entire lens system.

RELATED APPLICATION

[0001] This application is based on application No. 2002-196168 filed inJapan on Jul. 4, 2002, the content of which is hereby incorporated byreference.

FIELD OF THE INVENTION

[0002] The present invention relates to an imaging device having animage sensor that converts, to electric signals, optical images formedon the light receiving surface of a charge coupled device (CCD), acomplementary metal-oxide semiconductor (CMOS) sensor or the like, andmore particularly, to an imaging device which is a principal element ofcameras incorporated in or externally attached to digital cameras,personal computers, mobile computers, mobile telephones, personaldigital assistances (PDAs) and the like. Specifically, the presentinvention relates to a compact imaging device having a zoom lens system.

DESCRIPTION OF THE PRIOR ART

[0003] In recent years, digital cameras have been rapidly becomingwidespread that convert an optical image to electronic signals by usingan image sensor such as a CCD or a CMOS sensor instead of silver halidefilm, convert the data to digital form, and record or transfer thedigitized data. In such digital cameras, since CCDs and CMOS sensorshaving high pixels such as two million pixels and three million pixelsare comparatively inexpensively provided recently, a high-performanceimaging device mounted with an image sensor is in greatly increasingdemand. In particular, a compact imaging device is desired that isprovided with a zoom lens system capable of performing zooming withoutany image quality degradation.

[0004] Further, in recent years, imaging devices have been becomingincorporated in or externally attached to personal computers, mobilecomputers, mobile telephones, PDAs and the like because of improvementsin the image processing capability of semiconductor elements and thelike, which spurs the demand for a high-performance imaging device.

[0005] As zoom lens systems used for such imaging devices, so-calledminus lead zoom lens systems in which the lens unit disposed on the mostobject side has a negative optical power are proposed in large numbers.Minus lead zoom lens systems have features such that they are easilymade wide-angle and that the lens back focal length necessary forinserting an optical low-pass filter is easily secured.

[0006] Conventional examples of minus lead zoom lens systems includezoom lens systems proposed as taking lens systems for film-basedcameras. However, in these zoom lens systems, since the exit pupil ofthe lens system in the shortest focal length condition is situatedcomparatively near the image plane, it does not match with the pupil ofthe microlens provided so as to correspond to each pixel of the imagesensor having high pixels, so that a sufficient quantity of peripherallight cannot be secured. In addition, since the position of the exitpupil largely varies during zooming, the setting of the pupil of themicrolens is difficult. Further, since required optical performance suchas spatial frequency characteristics is completely different betweensilver halide film and image sensors to begin with, optical performancerequired of image sensors cannot be sufficiently secured. For thesereasons, there has emerged a need for the development of a dedicatedzoom lens system optimized for imaging devices having an image sensor.

[0007] On the other hand, to reduce the size of the imaging device, aproposal has been made to attain size reduction without any change inoptical path length by bending the zoom lens system in the middle of theoptical path. For example, Japanese Laid-Open Patent Application No.H11-196303 proposes an imaging device where in a minus lead zoom lenssystem, a reflecting surface is provided on the optical path and theoptical path is bent substantially 90 degrees by the reflecting surfaceand then forms an optical image on the image sensor by way of movablelens units. The imaging device disclosed by this application has astructure that a reflecting surface is provided on the image side of afixed lens element of a negative meniscus configuration and the opticalpath is bent substantially 90 degrees by the reflecting surface and thenreaches the image sensor by way of two movable positive lens units and afixed positive lens unit.

[0008] As another example, Japanese Laid-Open Patent Application No.H11-258678 discloses a structure that a reflecting surface is providedon the image side of a fixed lens element of a negative meniscusconfiguration and a movable positive lens unit and the optical path isbent substantially 90 degrees by the reflecting surface and then reachesthe image sensor by way of a positive lens unit.

[0009] However, in these two applications, only the lens barrelstructure is disclosed and no specific zoom lens system structure isshown. It is difficult to reduce the overall size of imaging deviceshaving a zoom lens system unless the zoom lens system taking up thelargest space in volume is optimized.

[0010] Moreover, although demand for cost reduction of these imagingdevices are strong, there is a limitation to the cost reduction.

OBJECT AND SUMMARY

[0011] An object of the present invention is to provide an improvedimaging device.

[0012] Another object of the present invention is to provide an imagingdevice that is compact and can be manufactured at low cost althoughhaving a high-performance and high-magnification zoom lens system.

[0013] The above-mentioned objects are attained by an imaging devicehaving the following structure:

[0014] An imaging device comprising: a zoom lens system having aplurality of lens units and forming an optical image of an object so asto continuously optically zoom by varying distances between the lensunit; and an image sensor converting the optical image formed by thezoom lens system to an electric signal, wherein the zoom lens systemcomprises from an object side: a first lens unit being overall negativeand including a reflecting surface that bends a luminous fluxsubstantially 90 degrees; and a second lens unit disposed with avariable air distance from the first lens unit, and having an opticalpower, and at least one lens element made of resin is included in theentire lens system.

[0015] Moreover, another aspect of the present invention is a digitalcamera including the above-described imaging device. While the termdigital camera conventionally denotes cameras that record only opticalstill images, cameras that can handle moving images as well and homedigital video cameras have also been proposed and at present, there isno distinction between cameras that record only still images and camerasthat can handle moving images as well. Therefore, in the followingdescription, the term digital camera includes all of the cameras such asdigital still cameras and digital movie cameras where an imaging devicehaving an image sensor that converts optical images formed on the lightreceiving surface of the image sensor to electric signals is a principalelement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] This and other objects and features of this invention will becomeclear from the following description, taken in conjunction with thepreferred embodiments with reference to the accompanied drawings inwhich:

[0017]FIG. 1 is a lens construction view of a first embodiment (firstexample);

[0018]FIG. 2 is a lens construction view of a second embodiment (secondexample);

[0019]FIG. 3 is a lens construction view of a third embodiment (thirdexample);

[0020]FIG. 4 is a lens construction view of a fourth embodiment (fourthexample);

[0021]FIG. 5 is a lens construction view of a fifth embodiment (fifthexample);

[0022]FIGS. 6A to 6I are graphic representations of aberrations of thefirst embodiment in in-focus state at infinity;

[0023]FIGS. 7A to 7I are graphic representations of aberrations of thesecond embodiment in in-focus state at infinity;

[0024]FIGS. 8A to 8I are graphic representations of aberrations of thethird embodiment in in-focus state at infinity;

[0025]FIGS. 9A to 9I are graphic representations of aberrations of thefourth embodiment in in-focus state at infinity;

[0026]FIGS. 10A to 10I are graphic representations of aberrations of thefifth embodiment in in-focus state at infinity; and

[0027]FIG. 11 is a construction view showing the present invention inoutline.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Referring to the drawings, an embodiment of the present inventionwill be described.

[0029] An imaging device according to the embodiment of the presentinvention comprises, for example as shown in FIG. 11, from the objectside (subject side): a zoom lens system TL forming an optical image ofan object so as to zoom, an optical low-pass filter LPF, and an imagesensor SR converting the optical image formed by the zoom lens system TLto electric signals. The zoom lens system comprises a first lens unitGr1 including a prism PR having a reflecting surface inside, andsucceeding lens units. The imaging device is a principal element ofcameras incorporated in or externally attached to digital cameras, videocameras, personal computers, mobile computers, mobile telephones, PDAsand the like.

[0030] The zoom lens system TL comprises a plurality of lens unitsincluding the first lens unit Gr1. The size of the optical image can bevaried by varying the distances between the lens units. The first lensunit Gr1 has a negative optical power, and includes the prism PR thatbends the optical axis of the object light substantially 90 degrees.

[0031] The optical low-pass filter LPF has a specific cutoff frequencyfor adjusting the spatial frequency characteristics of the taking lenssystem to thereby eliminate the color moire generated in the imagesensor. The optical low-pass filter of the embodiment is a birefringentlow-pass filter formed by laminating a birefringent material such ascrystal having its crystallographic axis adjusted in a predetermineddirection, wave plates changing the plane of polarization, or the like.As the optical low-pass filter, a phase low-pass filter or the like maybe adopted that attains necessary optical cutoff frequencycharacteristics by a diffraction effect.

[0032] The image sensor SR comprises a CCD having a plurality of pixels,and converts the optical image formed by the zoom lens system toelectric signals by the CCD. The signals generated by the image sensorSR undergo predetermined digital image processing or image compressionprocessing as required, and are recorded into a memory (a semiconductormemory, an optical disk, etc.) as digital video signals or in somecases, transferred to another apparatus through a cable or by beingconverted to infrared signals. A CMOS sensor may be used instead of aCCD.

[0033] FIGS. 1 to 5 are construction views showing the lensarrangements, in the shortest focal length condition, of the zoom lenssystems included in imaging devices according to a first to a fifthembodiment of the present invention. In these figures, the prism PRhaving an internal reflection surface is illustrated as a plane-parallelplate, and the optical path is illustrated as a straight line.

[0034] A zoom lens system of the first embodiment comprises from theobject side to the image side: a first lens unit Gr1 including a firstlens element L1 being a negative meniscus lens element convex to theobject side, and a plate PR corresponding to the prism; a second lensunit Gr2 including a second lens element L2 of a negative meniscusconfiguration convex to the object side and a third lens element L3 of apositive meniscus configuration convex to the object side; a diaphragmST; a third lens unit Gr3 including a first doublet lens element DL1consisting of a fourth lens element L4 of a bi-convex configuration anda fifth lens element L5 of a bi-concave configuration; and a fourth lensunit Gr4 including a sixth lens element L6 of a negative meniscusconfiguration concave to the object side. On the image side of thefourth lens unit Gr4 of this zoom lens system, a plane-parallel plateLPF corresponding to the optical low-pass filter is disposed.

[0035] In this zoom lens system, in zooming from the shortest focallength condition to the longest focal length condition, the first lensunit Gr1 is fixed with respect to the image plane, the second lens unitGr2 moves so as to draw a locus of a U-tun convex to the image side suchthat it first moves toward the image side and then moves toward theobject side, the third lens unit Gr3 substantially monotonously movestoward the object side integrally with the diaphragm ST disposed on theobject side of the third lens unit Gr3, the fourth lens unit Gr4substantially monotonously moves toward the image side, and theplane-parallel plate LPF is fixed with respect to the image plane.

[0036] Of the surfaces of the lens elements, both side surfaces of thesecond lens element L2, the image side surface of the fifth lens elementL5 and both side surfaces of the sixth lens element L6 are aspherical.The sixth lens element L6 included in the fourth lens unit Gr4 is aresin lens element.

[0037] A zoom lens system of the second embodiment comprises from theobject side to the image side: a first lens unit Gr1 including a firstlens element L1 being a negative meniscus lens element convex to theobject side, a second lens element L2 of a positive meniscusconfiguration convex to the object side, and a plate PR corresponding tothe prism; a second lens unit Gr2 including a third lens element L3 of anegative meniscus configuration convex to the object side and a fourthlens element L4 of a positive meniscus configuration convex to theobject side; a diaphragm ST; a third lens unit Gr3 including a firstdoublet lens element DL consisting of a fifth lens element L5 of abi-convex configuration and a sixth lens element L6 of a bi-concaveconfiguration; and a fourth lens unit Gr4 including a seventh lenselement L7 of a negative meniscus configuration concave to the objectside. On the image side of the fourth lens unit Gr4 of this zoom lenssystem, a plane-parallel plate LPF corresponding to the optical low-passfilter is disposed.

[0038] In this zoom lens system, in zooming from the shortest focallength condition to the longest focal length condition, the first lensunit Gr1 is fixed with respect to the image plane, the second lens unitGr2 moves so as to draw a locus of a U-turn convex to the image sidesuch that it first moves toward the image side and then moves toward theobject side, the third lens unit Gr3 substantially monotonously movestoward the object side integrally with the diaphragm ST disposed on theobject side of the third lens unit Gr3, the fourth lens unit Gr4substantially monotonously moves toward the image side, and theplane-parallel plate LPF is fixed with respect to the image plane.

[0039] Of the surfaces of the lens elements, the image side surface ofthe third lens element L3, the image side surface of the fourth lenselement L4, the image side surface of the sixth lens element L6 and bothside surfaces of the seventh lens element L7 are aspherical. The fourthlens element L4 included in the second lens unit Gr2 is a resin lenselement.

[0040] A zoom lens system of the third embodiment comprises from theobject side to the image side: a first lens unit Gr1 including a firstlens element L1 being a negative meniscus lens element convex to theobject side, and a plate PR corresponding to the prism; a second lensunit Gr2 including a second lens element L2 of a bi-concaveconfiguration and a third lens element L3 of a positive meniscusconfiguration convex to the object side; a diaphragm ST; a third lensunit Gr3 including a first doublet lens element DL1 consisting of afourth lens element L4 of a bi-convex configuration and a fifth lenselement L5 of a bi-concave configuration, and a sixth lens element L6 ofa negative meniscus configuration convex to the object side; and afourth lens unit Gr4 including a seventh lens element L7 of a negativemeniscus configuration concave to the object side. On the image side ofthe fourth lens unit Gr4 of this zoom lens system, a plane-parallelplate LPF corresponding to the optical low-pass filter is disposed.

[0041] In this zoom lens system, in zooming from the shortest focallength condition to the longest focal length condition, the first lensunit Gr1 is fixed with respect to the image plane, the second lens unitGr2 moves so as to draw a locus of a U-turn convex to the image sidesuch that it first moves toward the image side and then moves toward theobject side, the third lens unit Gr3 substantially monotonously movestoward the object side integrally with the diaphragm ST disposed on theobject side of the third lens unit Gr3, the fourth lens unit Gr4substantially monotonously moves toward the image side, and theplane-parallel plate LPF is fixed with respect to the image plane.

[0042] Of the surfaces of the lens elements, the image side surface ofthe second lens element L2, the image side surface of the third lenselement L3, the image side surface of the sixth lens element L6 and bothside surfaces of the seventh lens element L7 are aspherical. The thirdlens element L3 included in the second lens unit Gr2, the sixth lenselement L6 included in the third lens unit Gr3 and the seventh lenselement L7 included in the fourth lens unit Gr4 are resin lens elements.

[0043] A zoom lens system of the fourth embodiment comprises from theobject side to the image side: a first lens unit Gr1 including a firstlens element L1 being a negative meniscus lens element convex to theobject side, a second lens element L2 of a positive meniscusconfiguration convex to the object side, and a plate PR corresponding tothe prism; a second lens unit Gr2 including a third lens element L3 of abi-concave configuration and a fourth lens element L4 of a positivemeniscus configuration convex to the object side; a diaphragm ST; athird lens unit Gr3 including a first doublet lens element DL1consisting of a fifth lens element L5 of a bi-convex configuration and asixth lens element L6 of a bi-concave configuration; and a fourth lensunit Gr4 including a seventh lens element L7 of a positive meniscusconfiguration concave to the object side. On the image side of thefourth lens element Gr4 of this zoom lens system, a plane-parallel plateLPF corresponding to the optical low-pass filter is disposed.

[0044] In this zoom lens system, in zooming from the shortest focallength condition to the longest focal length condition, the first lensunit Gr1 is fixed with respect to the image plane, the second lens unitGr2 moves so as to draw a locus of a U-turn convex to the image sidesuch that it first moves toward the image side and then moves toward theobject side, the third lens unit Gr3 substantially monotonously movestoward the object side integrally with the diaphragm ST disposed on theobject side of the third lens unit Gr3, the fourth lens unit Gr4substantially monotonously moves toward the image side, and theplane-parallel plate LPF is fixed with respect to the image plane.

[0045] Of the surfaces of the lens elements, the object side surface ofthe second lens element L2, the image side surface of the third lenselement L3, the image side surface of the fourth lens element L4, theimage side surface of the sixth lens element L6 and both side surfacesof the seventh lens element L7 are aspherical. The seventh lens elementL7 included in the fourth lens unit Gr4 is a resin lens element.

[0046] A zoom lens system of the fifth embodiment comprises from theobject side to the image side: a first lens unit Gr1 including a firstlens element L1 being a negative meniscus lens element convex to theobject side, and a plate PR corresponding to the prism; a second lensunit Gr2 including a second lens element L2 of a bi-concaveconfiguration and a third lens element L3 of a positive meniscusconfiguration convex to the object side; a diaphragm ST; a third lensunit Gr3 including a first doublet lens element DL1 consisting of afourth lens element L4 of a bi-convex configuration and a fifth lenselement L5 of a bi-concave configuration; a fourth lens unit Gr4including a sixth lens element L6 of a negative meniscus configurationconcave to the object side; and a fifth lens unit Gr5 including aseventh lens element L7 of a bi-convex configuration. On the image sideof the fifth lens unit Gr5 of this zoom lens system, a plane-parallelplate LPF corresponding to the optical low-pass filter is disposed.

[0047] In this zoom lens system, in zooming from the shortest focallength condition to the longest focal length condition, the first lensunit Gr1 is fixed with respect to the image plane, the second lens unitGr2 moves so as to draw a locus of a U-turn convex to the image sidesuch that it first moves toward the image side and then moves toward theobject side, the third lens unit Gr3 substantially monotonously movestoward the object side integrally with the diaphragm ST disposed on theobject side of the third lens unit Gr3, the fourth lens unit Gr4substantially monotonously moves toward the image side, and the fifthlens unit Gr5 is fixed with respect to the image plane together with theplane-parallel plate LPF.

[0048] Of the surfaces of the lens elements, the image side surface ofthe third lens element L3, the image side surface of the fourth lenselement L4, the image side surface of the sixth lens element L6 and bothside surfaces of the seventh lens element L7 are aspherical. The thirdlens element L3 included in the second lens unit Gr2, the fifth lenselement L5 included in the third lens unit Gr3 and the sixth lenselement L6 included in the fourth lens unit Gr4 are resin lens elements.

[0049] In the zoom lens systems of these embodiments, the prism PRhaving a reflecting surface that bends the optical axis of the objectlight substantially 90 degrees is provided in the first lens unit. Bythus bending the optical axis of the object light substantially 90degrees, the apparent thickness of the imaging device can be reduced.

[0050] When a digital camera is taken as an example, the element thattakes up the largest volume in the apparatus is the imaging deviceincluding the zoom lens system. Particularly, when in digital cameras,optical elements such as lens elements and a diaphragm included in thezoom lens system are arranged in line without the direction of theoptical axis being changed like in conventional lens-shutter typefilm-based cameras, the size of the camera in the direction of thethickness substantially depends on the distance from the most objectside element of the zoom lens system to the image sensor included in theimaging device. However, the aberration correction level of imagingdevices have dramatically improved with the increase in the number ofpixels of image sensors in recent years. Consequently, the number oflens elements of the zoom lens systems included in imaging devices neverstop increasing, so that because of the thickness of the lens elements,it is difficult to reduce the thickness even when the camera is not used(in so-called collapsed condition).

[0051] On the contrary, by adopting the structure that the optical axisof the object light is bent substantially 90 degrees by the reflectingsurface like the zoom lens systems of the embodiments, the size of theimaging device in the direction of the thickness can be reduced to thedistance from the most object side lens element to the reflectingsurface when the camera is not used, so that the apparent thickness ofthe imaging device can be reduced. Moreover, by adopting the structurethat the optical axis of the object light substantially 90 degrees bythe reflecting surface, the optical path of the object light can befolded in the vicinity of the reflecting surface, so that space can beeffectively used and further size reduction of the imaging device can beattained.

[0052] It is desirable that the reflecting surface be disposed in thefirst lens unit Gr1. By disposing the reflecting surface in the firstlens unit Gr1 disposed on the most object side, the size of the imagingdevice in the direction of the thickness can be minimized.

[0053] It is desirable that the first lens unit Gr1 including thereflecting surface have a negative optical power. By the first lens unitGr1 having a negative optical power, the size of the reflecting surfacein the reflecting surface position can be reduced. Moreover, by adoptingthe structure that the first lens unit Gr1 has a negative optical power,the zoom lens system is of a so-called minus lead type. Minus lead typezoom lens systems are desirable because it is easy for them to adopt aretrofocus type structure in a wide focal length range and attain theimage-side telecentricity necessary for optical systems for formingoptical images on the image sensor.

[0054] While any of (a) an internal reflection prism (embodiments), (b)a surface reflection prism, (c) an internal reflection plane mirror and(d) a surface reflection mirror may be adopted as the reflectingsurface, (a) an internal reflection mirror is the most suitable. Byadopting an internal reflection prism, the object light passes throughthe medium of the prism, so that the axial distance when the objectlight passes through the prism is a reduced axial distance shorter thanthe normal air distance in accordance with the refractive index of themedium. For this reason, it is desirable that an internal reflectionprism be adopted as the structure of the reflecting surface because anoptically equivalent structure can be attained with a smaller space.

[0055] When the reflecting surface is an internal reflection prism, itis desirable that the material of the prism satisfy the followingcondition:

Np≧1.55  (1)

[0056] where Np is the refractive index of the material of the prism.

[0057] When the refractive index of the prism be lower than this range,the contribution to size reduction is small. Therefore, it isundesirable that the refractive index of the prism be lower than thisrange.

[0058] In addition to this range, it is desirable that the refractiveindex be within the following range:

Np≧1.7  (1)′

[0059] The reflecting surface is not necessarily a complete totalreflection surface. The reflectance of part of the reflecting surfacemay be appropriately adjusted so that part of the object light branchesoff so as to be incident on a sensor for metering or distancemeasurement. Moreover, the reflectance of the entire area of thereflecting surface may be appropriately adjusted so that the finderlight branches. While the incident surface and the exit surface of theprism are both plane in the embodiments, they may have an optical power.

[0060] It is desirable that not more than two lens elements be disposedon the object side of the reflecting surface. In a structure having inthe first lens unit the prism PR having a reflecting surface that bendsthe optical axis of the object light substantially 90 degrees, thethickness of the optical system substantially depends on the distancefrom the object side surface of the lens element disposed on the mostobject side to the reflecting surface. Therefore, by disposing not morethan two lens elements on the object side of the reflecting surface, athin optical system can be obtained. In particular, when the first lensunit Gr1 includes only one lens element and the reflecting surface, thedegree of freedom of the lens barrel structure can be increased, so thatcost reduction of the imaging device can be attained. When the firstlens unit Gr1 includes only two lens elements and the reflectingsurface, relative decentration aberration correction can be performed,which is advantageous in optical performance.

[0061] Further, it is desirable that the first lens unit Gr1 be fixedwith respect to the image plane during zooming. Since the first lensunit Gr1 includes the reflecting surface, moving it requires a largespace, and in particular, when the reflecting surface comprises a prism,it is necessary to move a prism having a large weight, so that a heavyburden is placed on the driving mechanism. Moreover, by the first lensunit Gr1 being fixed with respect to the image plane during zooming, anoptical system whose overall length does not vary can be obtained.Moreover, since the lens barrel structure can be simplified, costreduction of the imaging device can be attained. Further, by adoptingthe structure that the first lens unit Gr1 is fixed during zooming,particularly in digital cameras, it is easy to initialize the controlsystem for controlling the lens units movable during zooming, so thatthe time necessary for the camera to become ready to photograph when themain power is turned on can be reduced.

[0062] The zoom lens systems of the embodiments adopt a structure thatthe second lens unit Gr2 succeeding the first lens unit Gr1 having anegative optical power also has a negative optical power. This structureis desirable because it makes it easy to adopt the above-mentionedstructure that the first lens unit Gr1 is fixed.

[0063] Conditions desirable for the optical systems will be shown. It isdesirable that the optical systems of the above-described embodimentssatisfy the following condition (2):

−0.8<CP×(N′−N)/φw<0.8  (2)

[0064] where Cp is the curvature of the resin lens element, φw is theoverall optical power in the shortest focal length condition, N is therefractive index, to the d-line, of the object side medium of theaspherical surface, and N′ is the refractive index, to the d-line, ofthe image side medium of the aspherical surface.

[0065] The condition (2) defines the surface optical power of the resinlens element. When the surface optical power is too strong, aberrationsare degraded because of surface configuration changes due to temperaturechanges. When the lower limit of the condition (2) is exceeded, negativeoptical power is too strong, and when the upper limit thereof isexceeded, positive optical power is too strong, so that when the firstlens unit includes a resin lens element, mainly variation in fieldcurvature due to temperature changes is large. When the second lens unitincludes a resin lens element, mainly variation in spherical aberrationdue to temperature changes is large. When the third lens unit includes aresin lens element, mainly variation in spherical aberration, and comaaberration of a peripheral luminous flux due to temperature changes islarge.

[0066] When a resin lens element is used in the first lens unit, it isdesirable that the following condition (3) be satisfied:

|φp/φ1|<1.20  (3)

[0067] where φp is the optical power of the resin lens element and φ1 isthe optical power of the first lens unit.

[0068] The condition (3) defines the ratio between the optical power ofthe first lens unit and the optical power of the resin lens elementincluded in the first lens unit, and is a condition for keepingappropriate the aberration variation due to temperature changes. Whenthe upper limit of the condition (3) is exceeded, variation in fieldcurvature, particularly field curvature on the wide-angle side, due totemperature changes is large. For correction of aberrations generated inthe first lens unit, it is desirable to provide at least one positivelens element and one negative lens element.

[0069] When a resin lens element is used in the second lens unit, it isdesirable that the following condition (4) be satisfied:

|φp/φ2|<2.5  (4)

[0070] where φ2 is the optical power of the second lens unit.

[0071] The condition (4) defines the ratio between the optical power ofthe second lens unit and the optical power of the resin lens elementincluded in the second lens unit and is a condition for keepingappropriate the aberration variation due to temperature changes. Whenthe upper limit of the condition (4) is exceeded, variation in sphericalaberration, particularly spherical aberration on the telephoto side, dueto temperature changes is large. For correction of aberrations generatedin the second lens unit, it is desirable to provide at least onepositive lens element and one negative lens element.

[0072] While no lower limits are defined in the above conditions, thatthe values of the conditions are low means that the optical power of theresin lens element is weak, which is a desirable direction for theaberration variation due to temperature changes. However, this is noteffective for aberration correction at ordinary temperatures and theprovision of a resin lens element is meaningless. Therefore, when theresin lens element satisfies the following condition (5), it isessential that an aspherical surface be provided.

0≦|φp/φA|<0.45  (5)

[0073] where φA is the optical power of the lens unit including a resinlens element.

[0074] It is to be noted that an aspherical surface may be provided to aresin lens element exceeding the upper limit of the condition (5).

[0075] It is preferable that zoom lens system satisfy the followingcondition (6):

1.0<D/fw<2.6  (6)

[0076] where D represents an axial distance between surface at the mostobject side surface of the first lens unit and reflection surface; andfw represents a focal length of the entire zoom lens system in a wideangle condition.

[0077] The condition (6) defines the preferable relation the axialdistance between surface at the most object side surface of the firstlens unit and reflection surface. This condition (6) is required tominiaturize the entire optical system having reflection surface. If thelower limit of condition (6) were be transgressed, the optical power ofthe lens elements at the object side of the reflection surface would betoo strong. This would cause a distortion so large (especially thenegative distortion on the wide-angle end) that it would be impossibleto secure satisfactory optical performance. By contrast, if the upperlimit of condition (6) were to be transgressed, the axial distancebetween surface at the most object side surface of the first lens unitand reflection surface would be too long, which is undesirable in termof miniaturization. In addition to the above-mentioned range, it ispreferable that the following range (6)′ is fulfilled:

D/fw<2.2  (6)′

[0078] While the lens units of the embodiments comprise only refractivetype lens elements that deflect the incident ray by refraction (that is,lens elements of a type in which the incident ray is deflected at theinterface between media having different refractive indices), thepresent invention is not limited thereto. For example, the lens unitsmay comprise diffractive type lens elements that deflect the incidentray by diffraction, refractive-diffractive hybrid lens elements thatdeflect the incident ray by a combination of diffraction and refraction,or gradient index lens elements that deflect the incident ray by thedistribution of refractive index in the medium.

[0079] The construction of the zoom lens systems included in the imagingdevice embodying the present invention will be more concretely describedwith reference to construction data, graphic representations ofaberrations and the like. A first to a fifth example described here asexamples corresponds to the first to the fifth embodiments describedabove. The lens construction views (FIGS. 1 to 5) showing the first tothe fifth embodiments show the lens arrangements of the correspondingfirst to fifth examples.

[0080] In the construction data of the examples, ri (i=1, 2, 3, . . . )is the radius (mm) of curvature of the i-th surface counted from theobject side, di (i=1, 2, 3, . . . ) is the i-th axial distance (mm)counted from the object side, and Ni (i=1, 2, 3, . . . ) and vi (i=1, 2,3, . . . ) are the refractive index (Nd) and the Abbe number (vd), tothe d-line, of the i-th optical element counted from the object side. Inthe construction data, as the axial distances that vary during zooming,values in the shortest focal length condition (wide-angle limit, W), inthe middle focal length condition (middle, M) and in the longest focallength condition (telephoto limit, T) are shown. The overall focallengths (f, mm) and the f-numbers (FNO) in the focal length conditions(W), (M) and (T) are shown together with other data.

[0081] The surfaces whose radii of curvature ri are marked withasterisks are aspherical, and are defined by the following expression(AS) expressing the aspherical surface configuration. Aspherical data ofthe embodiments is shown as well. $\begin{matrix}{x = {\frac{C_{0}y^{2}}{1 + \sqrt{1 - {ɛ\quad C_{0}^{2}y^{2}}}} + {\sum{Aiy}^{i}}}} & ({AS})\end{matrix}$

[0082] where,

[0083] x represents the shape (mm) of the aspherical surface (i.e., thedisplacement along the optical axis at the height y in a directionperpendicular to the optical axis of the aspherical surface),

[0084] Co represents the curvature (mm⁻¹) of the reference asphericalsurface of the aspherical surface,

[0085] y represents the height in a direction perpendicular to theoptical axis,

[0086] ε represents the quadric surface parameter, and

[0087] Ai represents the aspherical coefficient of order i.

EXAMPLE 1

[0088] f = 4.5 − 7.9 − 12.9 Fno. = 2.1 − 2.86 − 3.78 [Radius of [Axial[Refractive [Abbe Curvature] Distance] Index(Nd)] Number(vd)] r1 =131.891 d1 = 0.800 N1 = 1.51742 v1 = 52.41 r2 = 11.659 d2 = 1.650 r3 = ∞d3 = 8.000 N2 = 1.84666 v2 = 23.82 r4 = ∞ d4 = 1.500 r5* = 35.321 d5 =0.800 N3 = 1.52200 v3 = 52.20 r6* = 4.893 d6 = 1.276 r7 = 7.568 d7 =2.000 N4 = 1.84666 v4 = 23.82 r8 = 12.453 d8 = 11.029 − 3.671 − 0.998 r9= ∞ d9 = 0.6500 r10 = 5.991 d10 = 4.909 N5 = 1.75450 v5 = 51.57 r11 =−9.320 d11 = 0.010 N6 = 1.51400 v6 = 42.83 r12 = −9.320 d12 = 1.400 N7 =1.84666 v7 = 23.82 r13* = 26.705 d13 = 1.370 − 6.910 − 12.832 r14* =−16.667 d14 = 3.678 N8 = 1.52510 v8 = 56.38 r15* = −6.042 d15 = 4.129 −3.385 − 2.697 r16 = ∞ d16 = 1.500 N9 = 1.51680 v9 = 64.20 r17 = ∞[Aspherical Coefficient] r5* ε = 0.10000000E+01 A4 = 0.43313297E−03 A6 =−0.10070798E−03 A8 = 0.84126830E−05 A10 = −0.26384097E−06 r6* ε =0.10000000E+01 A4 = −0.30789841E−03 A6 = −0.11170196E−03 A8 =0.66705245E−05 A10 = −0.24941305E−06 r13* ε = 0.10000000E+01 A4 =0.15633769E−02 A6 = 0.51050129E−04 A8 = 0.24266581E−06 A10 =0.67988002E−06 r14* ε =0.10000000E+01 A4 = −0.12218564E−02 A6 =0.25134426E−03 A8 = −0.53931767E−04 A10 = 0.43794320E−05 r15* ε =0.10000000E+01 A4 = 0.94953834E−03 A6 = −0.27258786E−04 A8 =0.28920117E−05

EXAMPLE 2

[0089] f = 4.5 − 7.9 − 12.9 Fno. = 2.0 − 2.85 − 3.74 [Radius of [Axial[Refractive [Abbe Curvature] Distance] Index(Nd)] Number(vd)] r1 =33.725 d1 = 0.800 N1 = 1.85000 v1 = 40.04 r2 = 11.351 d2 = 1.200 r3 =25.554 d3 = 1.458 N2 = 1.75450 v2 = 51.57 r4 = 37.693 d4 = 0.800 r5 = ∞d5 = 8.200 N3 = 1.84666 v3 = 23.82 r6 = ∞ d6 = 1.500 − 3.420 − 1.500 r7= 97.822 d7 = 0.800 N4 = 1.52510 v4 = 56.38 r8* = 5.111 d8 = 0.743 r9 =6.467 d9 = 2.000 N5 = 1.84666 v5 = 23.82 r10 = 10.975 d10 = 10.550 −4.249 − 1.028 r11 = ∞ d11 = 0.650 r12 = 6.194 d12 = 5.604 N6 = 1.75450v6 = 51.57 r13 = −6.781 d13 = 0.010 N7 = 1.51400 v7 = 42.83 r14 = −6.781d14 = 1.183 N8 = 1.84666 v8 = 23.82 r15* = 38.043 d15 = 3.186 − 8.555 −13.974 r16* = 16.667 d16 = 3.812 N9 = 1.77250 v9 = 49.77 r17* = −5.893d17 = 2.712 − 1.724 − 1.447 r18 = ∞ d18 = 1.500 N10 = 1.51680 v10 =64.20 r19 =∞ [Aspherical Coefficient] r8* ε = 0.10000000E+01 A4 =−0.15428275E−03 A6 = −0.42877249E−04 A8 = 0.15793970E−06 A10 =−0.20720675E−07 r10* ε = 0.10000000E+01 A4 = −0.64995991E−04 A6 =0.17094079E−04 A8 = −0.16152162E−07 r15* ε = 0.10000000E+01 A4 =0.13775987E−02 A6 = 0.47166979E−04 A8 = 0.20857832E−05 A10 =0.23951237E−06 r16* ε = 0.10000000E+01 A4 = −0.20963217E−02 A6 =0.74122201E−04 A8 = −0.11877575E−04 A10 = 0.53768544E−06 r17* ε =0.10000000E+01 A4 = 0.80770597E−04 A6 = 0.42148914E−05 A8 =0.60309537E−07

EXAMPLE 3

[0090] f = 4.5 − 7.9 − 12.9 Fno. = 2.0 − 2.81 − 3.67 [Radius [Axial[Refractive [Abbe of Curvature] Distance] Index(Nd)] Number(vd)] r1 =15.797 d1 = 0.800 N1 = 1.58913 v1 = 61.11 r2 = 7.557 d2 = 2.700 r3 = ∞d3 = 8.009 N2 = 1.84666 v2 = 23.82 r4 = ∞ d4 = 1.500 − 3.160 − 1.500 r5= −26.368 d5 = 0.800 N3 = 1.48749 v3 = 70.44 r6* = 4.708 d6 = 0.518 r7 =5.361 d7 = 2.154 N4 = 1.85000 v4 = 40.04 r8* = 10.802 d8 = 11.235 −4.910 − 1.331 r9 = ∞ d9 = 0.650 r10 = 6.699 d10 = 4.000 N5 = 1.75450 v5= 51.57 r11 = −9.744 d11 = 0.010 N6 = 1.51400 v6 = 42.83 r12 = −9.744d12 = 0.800 N7 = 1.79850 v7 = 22.60 r13 = 67.530 d13 = 0.537 r14 =28.497 d14 = 0.800 N8 = 1.58340 v8 = 30.23 r15* = 18.947 d15 = 2.612 −8.560 − 14.167 r16* = − 30.752 d16 = 4.200 N9 = 1.52510 v9 = 56.38 r17*= −5.241] d17 = 2.934 − 1.651 − 1.283 r18 = ∞ d18 = 1.500 N10 = 1.51680v10 = 64.20 r19 = ∞ [Aspherical Coefficient] r6* ε = 0.10000000E+01 A4 =−0.10145481E−02 A6 = −0.72075706E−04 A8 = −0.19174089E−05 A10 =−0.46087898E−07 r8* ε = 0.10000000E+01 A4 = 0.70130028E−03 A6 =0.46972417E−04 A8 = 0.33943302E-05 r15* ε = 0.10000000E+01 A4 =0.14752106E−02 A6 = 0.55770047E−04 A8 = −0.10845300E−05 A10 = 00.44294001E−06 r16* ε = 0.10000000E+01 A4 = −0.1 8942226E−02 A6 =0.69566995E−04 A8 = −0.13206893E−04 A10 = 0.73140343E−06 r17* ε =0.10000000E+01 A4 = 0.74167453E−03 A6 = −0.16789975E−04 A8 =0.14074200E−05

EXAMPLE 4

[0091] f = 4.5 − 7.9 − 12.9 Fno. = 2.0 − 2.88 − 3.77 [Radius [Axial[Refractive [Abbe of Curvature] Distance] Index(Nd)] Number(vd)] r1 =24.847 d1 = 0.800 N1 = 1.85026 v1 = 32.15 r2 = 9.507 d2 = 1.200 r3* =18.529 d3 = 1.878 N2 = 1.52200 v2 = 52.20 r4 = 37.877 d4 = 0.800 r5 = ∞d5 = 8.200 N3 = 1.84666 v3 = 23.82 r6 = ∞ d6 = 1.500 − 3.255 − 1.500 r7=−23.840 d7 = 0.800 N4 = 1.52200 v4 = 52.20 r8* = 5.612 d8 = 0.500 r9* =6.897 d9 = 2.300 N5 = 1.84666 v5 = 23.82 r10* = 17.332 d10 = 11.012 −4.659 − 1.072 r11 = ∞ d11 = 0.650 r12 = 6.160 d12 = 6.000 N6 = 1.75450v6 = 51.57 r13 = −6.615 d13 = 0.010 N7 = 1.51400 v7 = 42.83 r14 = −6.615d14 = 0.969 N8 = 1.84666 v8 = 23.82 r15* = 29.536 d15 = 1.496 − 7.489 −12.982 r16* = −31.130 d16 = 4.200 N9 = 1.52510 v9 = 56.38 r17* = 5.934d17 = 3.226 − 1.831 − 1.680 r18 = ∞ d18 = 1.500 N10 = 1.51680 v10 =64.20 r19 = ∞ [Aspherical Coefficient] r3* ε = 0.10000000E+01 A4 =0.11455958E−03 A6 = −0.33371789E−06 A8 = 0.16291474E−07 r8 ε =0.10000000E+01 A4 = 0.11930738E-03 A6 = −0.41125994E−04 A8 =0.93638465E−06 A9 = −0.22174114E−07 r10* ε = 0.10000000E+01 A4 =−0.62127445E−04 A6 = 0.14433401E−04 A8 = −0.23787289E−06 r15* ε =0.10000000E+01 A4 = 0.15502859E−02 A6 = 0.47738830E−04 A8 =0.42055482E−05 A10 = 0.17243267E−06 r16* ε = 0.10000000E+01 A4 =−0.17058224E−02 A6 = 0.76334079E−04 A8 = −0.14552475E−04 A10 =0.69411194E−06 r17* ε = 0.10000000E+01 A4 = 0.88231293E−04 A6 =−0.18063594E−04 A8 = 0.70394395E−06

EXAMPLE 5

[0092] f = 4.5 − 7.9 − 12.9 Fno. = 2.0 − 2.69 − 3.45 [Radius [Axial[Refractive [Abbe of Curvature] Distance] Index(Nd)] Number(vd)] r1 =29.225 d1 = 0.800 N1 = 1.58913 v1 = 61.11 r2 = 9.824 d2 = 2.288 r3 = ∞d3 = 8.000 N2 = 1.84666 v2 = 23.82 r4 = ∞ d4 = 1.500 − 4.764 − 1.500 r5= 37.705 d5 = 0.800 N3 = 1.48749 v3 = 70.44 r6* = 4.423 d6 = 0.500 r7 =5.513 d7 = 2.00 N4 = 1.85000 v4 = 40.04 r8* = 8.515 d8 = 12.201 − 3.853− 1.149 r9 = ∞ d9 = 0.650 r10 = 6.604 d10 = 4.885 N5 = 1.75450 v5 =51.57 r11 = 7.480 d11 = 0.010 N6 = 1.51400 v6 = 42.83 r12 = −7.480 d12 =0.800 N7 = 1.79850 v7 = 22.60 r13 = −19.278 d13 = 0.900 − 1.200 − 1.501r14 = −7.554 d14 = 0.800 N8 = 1.58340 v8 = 30.23 r15* = 153.332 d15 =2.658 − 7.442 − 13.108 r16* = 7.127 d16 = 4.046 N9 = 1.52510 v9 = 56.38r17* = −66.811 d17 = 1.000 r18 = ∞ d18 = 1.500 N10 = 1.51680 v10 = 64.20r19 = ∞ [Aspherical Coefficient] r6* ε = 0.10000000E+01 A4 =−0.13188674E−03 A6 = −0.11077449E−03 A8 = 0.36905376E−05 A10 =−0.29138999E−06 r8* ε = 0.10000000E+01 A4 = −0.72069648E−04 A6 =0.45751204E−04 A8 = 0.72652405E−06 r15* ε = 0.10000000E+01 A4 =0.15958174E−02 A6 = −0.11349576E−04 A8 = 0.19068718E−04 A10 =−0.94307372E−06 r16* ε = 0.10000000E+01 A4 = −0.20231807E−03 A6 =0.92943008E−04 A8 = −0.39179305E−05 A10 = 0.15776897E−06 r17* ε =0.10000000E+01 A4 = 0.11215385E−02 A6 = 0.29269875E−04 A8 =0.12347517E−04

[0093]FIGS. 6A to 6I through 10A to 10I which are graphicrepresentations of aberrations of the first to the fifth examples showaberrations of the zoom lens systems of the examples in in-focus stateat infinity. In these figures, (W), (M) and (T) show aberrations (fromthe left, spherical aberration, sine condition, astigmatism anddistortion; Y′(mm) is the maximum image height [corresponding to thedistance from the optical axis] on the image sensor) in the shortestfocal length condition, in the middle focal length condition and in thelongest focal length condition, respectively. In the graphicrepresentations of spherical aberration, the solid line (d) showsspherical aberration to the d-line, the chain line (g) shows sphericalaberration to the g-line, the chain double-dashed line (c) showsspherical aberration to the c-line, and the broken line (SC) shows sinecondition. In the graphic representations of astigmatism, the brokenline (DM) shows astigmatism on the meridional image plane, and the solidline (DS) shows astigmatism on the sagittal image plane. In the graphicrepresentations of distortion, the solid line shows distortion % to thed-line.

[0094] As described above, according to the zoom lens systems of theembodiments, an imaging device can be provided that is compact althoughhaving a high-performance and high-magnification zoom lens system.

[0095] Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodification depart from the scope of the present invention, they shouldbe construed as being included therein.

What is claimed is:
 1. An imaging device comprising: a zoom lens systemhaving a plurality of lens units and forming an optical image of anobject so as to continuously optically zoom by varying distances betweenthe lens unit; and an image sensor converting the optical image formedby the zoom lens system to an electric signal, wherein the zoom lenssystem comprises from an object side: a first lens unit being overallnegative and including a reflecting surface that bends a luminous fluxsubstantially 90 degrees; and a second lens unit disposed with avariable air distance from the first lens unit, and having an opticalpower, and wherein at least one lens element made of resin is includedin the entire lens system.
 2. An imaging device as claimed in claim 1,wherein the resin lens fulfills the following condition:−0.8<CP×(N′−N)/φw<0.8 where Cp is the curvature of the resin lenselement, φw is the overall optical power in the shortest focal lengthcondition, N is the refractive index, to the d-line, of the object sidemedium of the aspherical surface, and N′ is the refractive index, to thed-line, of the image side medium of the aspherical surface.
 3. Animaging device as claimed in claim 1, wherein the resin lens is includedin the first lens unit.
 4. An imaging device as claimed in claim 3,wherein the zoom lens system fulfills the following condition:|φp/φ1|<1.20 where φp is the optical power of the resin lens element andφ1 is the optical power of the first lens unit.
 5. An imaging device asclaimed in claim 1, wherein the resin lens is included in the secondlens unit.
 6. An imaging device as claimed in claim 5, wherein the zoomlens system fulfills the following condition: |φp/φ2|<2.5 where φp isthe optical power of the resin lens element and φ2 is the optical powerof the second lens unit.
 7. An imaging device as claimed in claim 1,wherein the first lens unit includes a right-angle prism having aninternal reflecting surface as the reflecting surface.
 8. An imagingdevice as claimed in claim 7, wherein the following condition issatisfied: Np≧1.55 where Np is a refractive index to a d-line of theright-angle prism.
 9. An imaging device as claimed in claim 1, whereinthe second lens unit disposed with a variable air distance from thefirst lens unit, and having a negative optical power.
 10. An imagingdevice as claimed in claim 1, wherein the zoom lens system has not morethan two lens elements disposed on the object side of the reflectingsurface.
 11. An imaging device as claimed in claim 10, wherein the zoomlens system has only one lens element disposed on the object side of thereflecting surface.
 12. An imaging device as claimed in claim 1, whereinthe resin lens fulfills the following condition: 1.0<D/fw<2.6 where Drepresents an axial distance between surface at the most object sidesurface of the first lens unit and reflection surface; and fw representsa focal length of the entire zoom lens system in a wide angle condition.13. A camera comprising: an imaging device having a zoom lens system aplurality of lens units and forming an optical image of an object so asto continuously optically zoom by varying distances between the lensunit and an image sensor converting the optical image formed by the zoomlens system to an electric signal, wherein the zoom lens systemcomprises from an object side: a first lens unit being overall negativeand including a reflecting surface that bends a luminous fluxsubstantially 90 degrees; and a second lens unit disposed with avariable air distance from the first lens unit, and having an opticalpower, and wherein at least one lens element made of resin is includedin the entire lens system.
 14. A camera as claimed in claim 13, whereinthe resin lens fulfills the following condition: −0.8<CP×(N′−N)/φw<0.8where Cp is the curvature of the resin lens element, φw is the overalloptical power in the shortest focal length condition, N is therefractive index, to the d-line, of the object side medium of theaspherical surface, and N′ is the refractive index, to the d-line, ofthe image side medium of the aspherical surface.
 15. A camera as claimedin claim 13, wherein the resin lens is included in the first lens unit.16. A camera as claimed in claim 15, wherein the zoom lens systemfulfills the following condition: |φp/φ1|<1.20 where φp is the opticalpower of the resin lens element and φ1 is the optical power of the firstlens unit.
 17. A camera as claimed in claim 13, wherein the resin lensis included in the second lens unit.
 18. A camera as claimed in claim17, wherein the zoom lens system fulfills the following condition:|φp/φ2|<2.5 where φp is the optical power of the resin lens element andφ2 is the optical power of the second lens unit.
 19. A camera as claimedin claim 13, wherein the first lens unit includes a right-angle prismhaving an internal reflecting surface as the reflecting surface.
 20. Acamera as claimed in claim 19, wherein the following condition issatisfied: Np≧1.55 where Np is a refractive index to a d-line of theright-angle prism.
 21. A camera as claimed in claim 13, wherein thesecond lens unit disposed with a variable air distance from the firstlens unit, and having a negative optical power.
 22. A camera as claimedin claim 13, wherein the zoom lens system has not more than two lenselements disposed on the object side of the reflecting surface.
 23. Acamera as claimed in claim 13, wherein the zoom lens system has only onelens element disposed on the object side of the reflecting surface. 24.A camera as claimed in claim 13, wherein the resin lens fulfills thefollowing condition: 1.0<D/fw<2.6 where D represents an axial distancebetween surface at the most object side surface of the first lens unitand reflection surface; and fw represents a focal length of the entirezoom lens system in a wide angle condition.